The prism beam expander has advantages including compact structure, simple alignment, low costs, and minimized chromatic aberration. The most important application of the prism beam expander is to realize one-dimensional beam expansion and collimation for the laser beam before the incidence on the optical grating, while reducing the energy density of the beam and decreasing the divergence angle of the beam. In the high gain laser cavity, an ultra narrow linewidth laser may be achieved through a beam expander and an optical grating operated in Littrow configuration, while the loss of the laser efficiency may be minimal. Therefore, the prism beam expander is widely used in spectral linewidth narrowing modules of dye pulse lasers and excimer lasers. See U.S. Pat. No. 7,366,219.
In order to obtain narrower laser linewidth, the beam magnification needs to be increased. However, the beam magnification of the prism beam expander is associated with the number of prisms and the incidence angle of each prism. See Zhang Haibo et al., “Optimized design of the prism beam expander within the narrow linewidth excimer laser cavity,” Chinese Journal of Lasers 38, 1102008 (2011). On one hand, the beam magnification of the prism beam expander is sensitive to the prism incidence angle. In order to guarantee the beam magnification and the output laser linewidth in the prism beam expander, the incidence angle of each prism should be correctly demarcated. It is relatively easy to demarcate the incidence angle of a single prism without interference by adjacent prisms. The technical issue to be solved is to correctly demarcate the incidence angle of a plurality of adjacent prisms in the prism beam expander. On the other hand, the antireflection film of prisms has a good antireflection effect only in the scope of a narrow incidence angle. In order to improve the transmission of the beam of the coated prism and decrease laser cavity losses, the incidence angle of the prism should be consistent with the angle corresponding to the transmission peak of the prism, and the incidence angle of the prism should also be correctly demarcated. In addition, since the pitching of the prism affects the output energy of the laser, in order to improve the laser efficiency, the pitching of each prism should be tuned so that each prism in the prism beam expander is parallel.